1. Field of the Invention
The present invention relates to an inorganic waterborne coating agent which forms a thin, super-hydrophilic, transparent, and inorganic coated layer when applied to the surface of an organic or inorganic base material, and more particularly, to an inorganic waterborne coating agent and its aqueous solution excellent in antifouling property.
2. Description of the Related Art
Coating agents aimed at preventing or reducing fouling of base materials when applied to a coating object such as an organic or inorganic base material, have been well-known. Among such coating agents, a hydrophilic coating agent is well-known for its excellent antifouling property, capable of forming a continuously-wet surface by absorbing water from the air so that the cleaning thereof is facilitated by wiping out the coated surface. The most publicly well-known hydrophilic coating agent is the compound employing titania as a photocatalyst (for example, Japanese Patents No. 2923902, No. 2865065, and No. 2756474 by TOTO Ltd.).
However, the use of a photocatalytic material is limited because: requiring ultraviolet ray; in order to be applied onto an organic base material, requiring various primer treatments for preventing the organic base material from corrosion caused by photocatalytic reaction because the organic base material itself may be decomposed; having difficulty in ensuring its transparency when coating a transparent glass surface (turbidity may occur when the amount of titanium dioxide is increased; the effect may be deteriorated when the amount of titanium dioxide is decreased for higher transparency); and having low adhesion strength to a base material.
Also, as other coating agents for, for example, automobile body surface painting, such as a wax, a polysilazane-based glass coating agent, and a fluorine-based coating agent have been well-known, and they are applied for maintaining gloss and protecting organic coating films. However, an organic substance such as a wax may further amplify the problem of oxidation and organic contamination, thereby requiring to be periodically removed for recoating. Furthermore, oil contained in the wax may leak out due to rainfall, causing black streaks on the automobile body. These black streaks are difficult to be eliminated.
In addition, the polysilazane-based glass coating agent hardens as time goes by, and may cause cracks, peelings and breaks of the surface due to its thinness and/or its coefficient of thermal expansion (CTE) different from that of the automotive organic coating film. Once a crack occurs, it is difficult to repair it as well as to remove the contaminant proceeded thereinto. Also, these polysilazane-based glass coating agents react to and harden from the contact with water in the air (hydrolysis), and thus requiring a particular technique in maintenance and construction thereof, resulting in expensive prices. There are various constraints in the range of use and the construction technique of these coating agents, and moreover, these agents use organic materials as a part of their solvents and binders. As a whole, they cannot be regarded as environmentally friendly or excellent in working environments.
For coating a glass that especially requires transparency and smoothness, these agents are impossible, or at least need a particular skill in handling, and thus can be regarded as impossible for application to such as existing glass and windshield for automobile.
And also, the surface of a windshield for automobile is mainly coated with fluorine-based water repellent, however, since the water repellent is weak against abrasion, it would be easily removed by the operation of windshield wipers. This would cause flaws on the coated surface, resulting in the water repellent becoming rather a reason for adhesion of fouling (such as oil film).
As mentioned above, conventional coating agents have considerable limits in range of use, conditions of use, place of application, time of application, and skill for application, and thus, the prices are necessarily high for users, resulting in a drawback of restricted range of use.
In addition, a stainless-steel as a base material has many advantages such as hardly rusting, having good figure, not needing paint, and thus the total price being inexpensive, and thereby being used in various fields. Stainless-steel is used with patterns produced by hairline, vibration, and blast finish on the surface thereof, for the purpose of design as well as covering prominence of flaws. In this case, prominence of flaws can be suppressed for a certain level, however, a new problem may occur in that fouling adhered on the surface of the stainless-steel are hard to be removed due to many unevenness produced thereon. The stainless-steel is therefore covered with coating of organic clear resin, however, the texture of gloss which a stainless-steel naturally possesses would be deteriorated, and at the same time, organic fouling of the same kind of the resin coating would easily adhere thereon and be hardly removed.
In view of the above problem residing in the prior arts, it is an object of the present invention to provide an inorganic waterborne coating agent and its aqueous solution:
(1) which achieves antifouling effect of the super-hydrophilic property without using titania as a photocatalyst, and, at the same time, does not need ultraviolet ray and can also be applied to an organic base material;
(2) which secures prevention of bad influence to the surface of base material, reduction of environmental loads in the process of manufacturing and applying thereof, and safety to human body;
(3) wherein, with the surface of the base material highly-hydrophilizated, the contaminant such as oil-based contaminant and inorganic dust adhered onto the surface of the base material can be removed easily with water, and at the same time, the antistatic effect can be achieved due to its dust-repelling property;(4) which can be applied by anyone (non-skilled) with ease without considering the base material being organic or inorganic, compared with conventional coating agents, such as photocatalyst and polysilazane-based glass coating agent that have limited range of use;(5) which has little limit in conditions of use and is inexpensive and able to be applied to any places, thereby achieving the original goal of antifouling property.